1. Field of the Invention
The present invention relates to an image forming cartridge and image forming apparatus using an electrophotographic method.
2. Description of the Related Art
In the conventional image forming apparatus employing the electrophtographic method, the image forming cartridge is provided in a manner so as to be freely detachable and attachable. The image forming cartridge has a photoreceptor drum inside the cartridge and also a charging unit, exposing unit, developing unit, transferring unit and cleaning unit in an area surrounding the photoreceptor drum. All of the above members are. covered by a cartridge case, thus making up the image forming cartridge.
Moreover, in the above photoreceptor drum, a rotary axis is fitted into a bearing section mounted at a center of a flange, thus causing the photoreceptor drum to be grounded (refer to Japanese Utility Model Application No. Sho 62-49175).
Configurations of the conventional image forming cartridge will be described below. FIG. 12 is a cross-sectional view describing configurations of main portions of the conventional image forming cartridge.
As shown in FIG. 12, a photoreceptor drum 3 is provided in a cartridge case 2 covering the entire image forming cartridge 1. The photoreceptor drum 3 is made up of an electric charge generating layer and an electric charge transferring layer formed on a conductive substrate composed of a cylinder-shaped aluminum alloy member or a like. Into both ends of the photoreceptor drum, drum supporting members 4 and 5 made of a metal or a conductive resin are inserted by the application of pressure or bonded. An axial section of the drum supporting member 4 is inserted, in an involved state, in a bearing hole 2a formed in the cartridge case 2 in a manner so as to be rotational. This enables the photoreceptor drum 3 to be supported by the bearing hole 2 so as to be freely rotational relative to the cartridge case 2. Moreover, a gear 6 is provided at a part of areas surrounding the drum supporting member 4.
Positioning pins 8, 9 are attached to a frame 7 making up the image forming apparatus. Positioning pins 8 and 9 extrude toward a direction of the inside of the apparatus. Each of the positioning pins 8 and 9 is fitted into a rotation center hole formed at a center of each of the drum supporting members 4 and 5. A ring-shaped conductive spring member 10 is attached to an end face inside the drum supporting member 4. The conductive spring member 10 is so disposed that its edge contacts inner faces surrounding the photoreceptor drum 3 and so that an extruding portion 10a extending from the edge of the conductive spring member 10 toward the center is in contact with an end portion of the positioning pin 8.
Thus, the photoreceptor drum 3 is electrically connected through the conductive spring member 10 and the positioning pin 8 to the frame 7 and is grounded through the frame 7.
However, if an error in out-of-roundness between an internally circumferential wall face making up the rotation center hole of the drum supporting member 4 and a circumferential face of the positioning pin 8 is large, when the drum supporting member 4 rotates at a time of the rotation of the photoreceptor drum 3, since the circumferential face of the positioning pin 8 contacts the internally circumferential wall face in a sliding manner, there is a risk of changes in rotation speed of the photoreceptor drum 3. Therefore, though a method is available in which a bearing is provided between the positioning pin 8 and the rotation center hole, since it causes an increase in the number of components, costs are increased.
On the other hand, by decreasing a thickness of the drum supporting member 4 to reduce an area contacting faces surrounding the positioning pin 8, it is made possible to decrease an amount of contact in a sliding manner. However, in the case of the drum supporting member 4 made of the conductive resin, if the contact area is made smaller, since the drum supporting member 4 has inferior conductivity compared with other drum supporting members made of conductive metals, stable grounding of the photoreceptor drum 3 is impossible. This causes a low image quality and also causes noise, thus producing the risk of malfunctions.
In view of the above, it is an object of the present invention to provide an image forming cartridge having configurations that enable a photoreceptor drum to rotate with a constant velocity and the photoreceptor drum to be stably grounded.
It is another object of the present invention to provide an image forming apparatus having configurations that enable the photoreceptor drum to rotate with a constant velocity and the photoreceptor drum to be stably grounded.
According to a first aspect of the present invention, there is provided an image forming cartridge having a photoreceptor drum placed in a cartridge case and being attached to an image forming apparatus through the cartridge case in a manner so as to be detachable and attachable, including:
an electrically conductive axial member placed on a rotation center axis in the photoreceptor drum and being supported by the cartridge case;
an electrically conductive drum supporting member placed on the axial member in a manner so as to be rotational and movable and supporting the photoreceptor drum on the axial member in a manner so as to be rotational;
a collar placed on a circumferential face near the drum supporting member of the axial member in a manner so as to be rotational and movable and being composed of a conductor so that the photoreceptor drum is grounded through the axial member;
a thrust supplying unit to give thrust to the photoreceptor drum to press the drum supporting member, by application of pressure and through the photoreceptor drum, on the collar so as to cause the drum supporting member to contact the collar; and
a stopper used to prevent the pressed collar from moving on the axial member.
In the foregoing, a preferable mode is one wherein the drum supporting member is formed of a conductive resin and has a cone-shaped placement hole used to reduce an area contacting faces surrounding the axial member.
Also, a preferable mode is one wherein an end of the axial member penetrates the cartridge case and the end of the axial member contacts, in a struck manner, an elastic member used for grounding which is fixed to a frame constituting the image forming apparatus.
Also, a preferable mode is one wherein the thrust supplying unit is made up of a helical gear for rotation which is fixed coaxially to an end of the photoreceptor drum and of a driving gear composed of other helical gear which engages with the helical gear.
Also, a preferable mode is one wherein the stopper is a ring member to be fixed to a face surrounding the axial member.
Also, a preferable mode is one wherein the stopper is a wall face disposed opposite to the collar of the cartridge case.
According to a second aspect of the present invention, there is provided an image forming cartridge having a photoreceptor drum placed in a cartridge case and being attached to an image forming apparatus through the cartridge case in a manner so as to be detachable and attachable, including:
a shaft placed on a rotation center axis in the photoreceptor drum, both ends of which is supported, in a fixed manner, by the cartridge case;
a drum supporting member composed of a conductive resin being fixed internally on the side of one end of the photoreceptor drum and being placed on a circumferential face on the side of the one end of the shaft in a manner so as to be rotational and movable and supporting the photoreceptor drum or the shaft in a manner so as to be rotational;
a collar placed on a circumferential face near the drum supporting member of the axial member in a manner so as to be rotational and movable and being composed of a conductor so that the photoreceptor drum is grounded through the axial member;
a helical gear being coaxially fixed to the other end of the photoreceptor drum and being placed on a circumferential face on the side of the other end of the shaft which engages with a helical gear for driving the image forming apparatus and gives thrust to the photoreceptor drum to press the drum supporting member, by application of pressure and through the photoreceptor drum, on the collar so as to cause the drum supporting member to contact the collar; and
a stopper used to prevent the pressed collar from moving on the axial member.
In the foregoing, a preferable mode is one wherein the drum supporting member has a cone-shaped placement hole used to reduce an area contacting faces surrounding the axial member and a small diameter portion contacting faces surrounding the shaft.
Also, a preferable mode is one wherein an end of the shaft penetrates the cartridge case and the end of the shaft contacts, in a struck manner, an elastic member used for grounding which is fixed to a frame constituting the image forming apparatus.
Also, a preferable mode is one wherein the stopper is a ring member to be fixed to a face surrounding the axial member.
Also, a preferable mode is one wherein the stopper is a wall face disposed opposite to the collar of the cartridge case.
According to a third aspect of the present invention, there is provided an image forming apparatus provided with a photoreceptor drum in a manner so as to be rotational, including:
an electrically conductive axial member being supported by an axis in a manner so as to be rotational on a rotation center axis in the photoreceptor drum;
an electrically conductive drum supporting member placed on the axial member in a manner so as to be rotational and movable and supporting the photoreceptor drum on the axial member in a manner so as to be rotational;
a collar placed on a circumferential face near the drum supporting member of the axial member in a manner so as to be rotational and movable and being composed of a conductor so that the photoreceptor drum is grounded through the axial member;
a thrust supplying unit to give thrust to the photoreceptor drum to press the drum supporting member, by application of pressure and through the photoreceptor drum, on the collar so as to cause the drum supporting member to contact the collar; and
a stopper used to prevent the pressed collar from moving on the axial member.
Also, a preferable mode is one wherein the drum supporting member is formed of a conductive resin and has a cone-shaped placement hole used to reduce an area contacting faces surrounding the axial member.
Also, a preferable mode is one wherein the thrust supplying unit is made up of a helical gear for rotation which is fixed coaxially to an end of the photoreceptor drum and of a driving gear composed of other helical gear which engages with the helical gear.
Furthermore, a preferable mode is one the stopper is a ring member to be fixed to a face surrounding the axial member.
With the above configuration, by causing the drum supporting member to contact the collar, the photoreceptor drum can be reliably grounded through the axial member. Therefore, it is possible to prevent the image quality from becoming low and the malfunction caused noise from occurring.
With another configuration, the photoreceptor drum can be reliably grounded by using the collar or a like and therefore the area contacting the axial member of the drum supporting member can be also made smaller. Therefore, the sliding resistance between the axial member and drum supporting member can be reduced, which enables the photoreceptor drum to be rotated smoothly and eliminates the need for attachment of the bearing.